Oral Mucosa Tissue Equivalents for the Treatment of Limbal Stem Cell Deficiency

Limbal stem cell deficiency approaches and limbal niche restoration

Approaches to limbal stem cell deficiency remain challenging, especially in bilateral cases, where healthy limbal stem cells are not accessible. While living-related allogeneic and allogeneic limbal stem cell sources have been utilized, their dependence on immunosuppression and its associated side effects pose significant limitations. Mucosal and mesenchymal stem cells have shown potential for differentiation into limbal stem cells and promoting corneal healing, primarily when cultured on the amniotic membrane or fibrin. However, none can fully replicate the original limbus. Innovations in surgical techniques, such as simple oral mucosal transplantation and subconjunctival or intrastromal mesenchymal stem cell injections, are emerging approaches. For successful limbal regeneration, both appropriate cells and suitable scaffolds are essential. Recent studies on decellularized and acellularized limbus models have demonstrated the potential to provide a three-dimensional native structure for cell seeding, retention, and differentiation. Creating a thin, evenly decellularized scaffold is a critical step in ensuring proper corneo-limbal slope formation, facilitating cell migration to the ocular surface. Harvesting the limbus, decellularization, and cell seeding are the three main steps in limbal reconstruction. Recent studies focus on microkeratome-assisted limbal harvesting to create a thin, even, and 360-degree limbal graft. This technique helps form an attached corneo-limbal interface, facilitating limbal stem cell migration. In the second step, acellularization is performed to preserve the extracellular matrix as much as possible, maintaining hemostasis and supporting paracrine interactions. The final steps involve recellularization and transplantation onto the eye. We summarize various limbal decellularization methods, their outcomes, and their potential in limbal reconstruction. More clinical studies are needed to validate this phase of limbal deficiency treatment.

Advancing Bilateral Limbal Deficiency Surgery: A Comprehensive Review of Innovations with Mucosal Cells

Besides alternative surgical methods for bilateral limbal deficiency, such as KLAL (keratolimbal allograft), living-related conjunctival limbal allograft (LR-CLAL), and keratoprosthesis, regenerative medicine often necessitates the use of alternative sources of limbal cells in cases where access to fellow eye source cells is limited. Mucosal cells are most commonly used to restore limbal tissue in such scenarios. Current techniques involving mucosal cells include cultivated oral mucosal transplantation (COMT), oral mucosal graft transplantation (OMGT), and simple oral mucosal transplantation (SOMT). COMT requires suspension of cells and a culturing process that is time-consuming and cost-prohibitive. In contrast, OMGT requires solely a strip of mucosal graft for transplanting into the deficient eye. The most recently developed practice, SOMT, in which chopped biopsy tissue is transplanted into the deficient area, compensates for problems associated with both COMT and OMGT, making the process of addressing bilateral limbal deficiency easy, time-saving, and affordable. Although some undesirable outcomes, such as angiogenesis, can occur post-transplantation, and the ultimate goal of differentiation into limbal epithelial stem cells may not be achieved, mucosal cell sources can be a good alternative for stabilizing the ocular surface. Some studies emphasize that co-culturing limbal niches in mucosal cell cultures can enhance differentiation capability. This concept highlights the importance of the limbal environment in the differentiation process. In this review, we demonstrate the ongoing changes in surgical technique trends and how they have made mucosal cell transplantation easier and more effective for limbal regeneration.

Profile of biological characterizations and clinical application of corneal stem/progenitor cells

Corneal stem/progenitor cells are typical adult stem/progenitor cells. The human cornea covers the front of the eyeball, which protects the eye from the outside environment while allowing vision. The location and function demand the cornea to maintain its transparency and to continuously renew its epithelial surface by replacing injured or aged cells through a rapid turnover process in which corneal stem/progenitor cells play an important role. Corneal stem/progenitor cells include mainly corneal epithelial stem cells, corneal endothelial cell progenitors and corneal stromal stem cells. Since the discovery of corneal epithelial stem cells (also known as limbal stem cells) in 1971, an increasing number of markers for corneal stem/progenitor cells have been proposed, but there is no consensus regarding the definitive markers for them. Therefore, the identification, isolation and cultivation of these cells remain challenging without a unified approach. In this review, we systematically introduce the profile of biological characterizations, such as anatomy, characteristics, isolation, cultivation and molecular markers, and clinical applications of the three categories of corneal stem/progenitor cells.

Application Prospect and Preliminary Exploration of GelMA in Corneal Stroma Regeneration

Corneal regeneration has become a prominent study area in recent decades. Because the corneal stroma contributes about 90% of the corneal thickness in the corneal structure, corneal stromal regeneration is critical for the treatment of cornea disease. Numerous materials, including deacetylated chitosan, hydrophilic gel, collagen, gelatin methacrylate (GelMA), serine protein, glycerol sebacate, and decellularized extracellular matrix, have been explored for keratocytes regeneration. GelMA is one of the most prominent materials, which is becoming more and more popular because of its outstanding three-dimensional scaffold structure, strong mechanics, good optical transmittance, and biocompatibility. This review discussed recent research on corneal stroma regeneration materials and related GelMA.

Human Oral Mucosal Fibroblasts from Limbal Stem Cell Deficient Patients as an Autologous Feeder Layer for Epithelial Cell Culture

PURPOSE

To investigate if human oral mucosal fibroblasts (HOMF) from patients with limbal stem cell deficiency (LSCD) can be used as an autologous feeder layer to support the culture of epithelial cells for potential clinical use.

METHODS

HOMF were isolated from oral mucosal biopsies obtained from the following groups of patients with LSCD: aniridia, mucous membrane pemphigoid (MMP), Stevens-Johnson syndrome (SJS), and ectodermal dysplasia (ED). The ability of these cells to support the culture of human limbal epithelial cells (HLE) was compared to that of HOMF from non-LSCD donors and 3T3s commonly used to culture epithelial cells for use in the clinic to treat LSCD.

RESULTS

HOMF were successfully obtained by explant culture for 3/3 aniridia patients, 3/3 MMP patients, 1/3 SJS patients, and 1/1 ED patients. All HOMF cultured from these LSCD groups supported the expansion of HLE with epithelial culture times and total colony forming efficiency (CFE) comparable to those achieved on HOMF isolated from donors without LSCD. PCR showed that all HLE cultured on LSCD donor HOMF expressed p63α, CK15, PAX6, CK12, and MUC16 as did HLE cultured on the control non-LSCD donor HOMF and 3T3s. Western blotting detected CK15 and MUC16 protein expression in all groups.

CONCLUSIONS

HOMF from patients with LSCD can be successfully used to support the expansion of epithelial cells. These cells may therefore be useful as autologous feeder fibroblasts for the expansion of epithelial cells for use in the clinic to treat LSCD.

Corneal supply and the use of technology to reduce its demand: A review

Recovery and access to end-of-life corneal tissue for corneal transplantation, training and research is globally maldistributed. The reasons for the maldistribution are complex and multifaceted, and not well defined or understood. Currently there are few solutions available to effectively address these issues. This review provides an overview of the system, key issues impacting recovery and allocation and emphasises how end-user ophthalmologists and researchers, with support from administrators and the wider sector, can assist in increasing access long-term through sustaining eye banks nationally and globally. We posit that prevention measures and improved surgical techniques, together with the development of novel therapies will play a significant role in reducing demand and enhance the equitable allocation of corneas.